Method of producing fine particle dispersions

ABSTRACT

A method of producing a fine particle dispersion characterized by having a dispersing step where, after fine particles have been sucked into a dispersing medium to prepare a suspension by a suction type stirring machine and bubbles have been removed from the suspension by a bubble removing means, the suspension is pressurized and introduced from the opposite directions so as to collide with each other, thereby dispersing the suspension.

TECHNICAL FIELD

The present invention relates to a method of producing an ultrafineparticle predispersion. More particularly, the present invention relatesto an ultrafine particle dispersion producing method capable ofproducing an ultrafine particle dispersion for polishing surfaces ofsemiconductor devices, magnetic recording media and so forth withoutusing a dispersant and without mixing a contaminant or the like into thedispersion.

BACKGROUND ART

Fine particles are used in various fields. For example, fine particlesused in burning in the field of electronic industry are required toimprove in purity, density, etc. For example, fine particles of bariumtitanate, which is a material used for a ceramic capacitor and the like,indispensably need to increase in purity to a high level or improve indensity in order to attain an improvement in performance of thecapacitor by stabilization of the burned configuration thereof.

Meanwhile, methods of producing semiconductor devices or magneticrecording media include precisely polishing surfaces to obtainmirror-finished surfaces. In these precision polishing methods, a fineparticle dispersion for polishing is used. In particular, semiconductordevices are now highly integrated and also increased in the number oflayers constituting a multilayered structure. Semiconductor deviceshaving a multilayered structure need to planarize the surface of aninterlayer insulator film formed between a pair of adjacent layers. Inthe semiconductor manufacturing process, the interlayer insulator filmis planarized by polishing. Meanwhile, metal wiring is formed by avacuum deposition means. In this case, it is necessary to smooth thedeposited wiring film by removing minute unevenness varying in size anddensity.

In the process of polishing an oxide film formed of silicon dioxide toobtain a flat surface, colloidal silica with potassium hydroxide addedthereto is used. In polishing a metal wiring film, the metal is polishedchemically and mechanically by using a slurry prepared by mixingtogether an abrasive and an oxidizing agent.

Fine particle dispersions used in the chemical/mechanical polishingmethod are produced by dispersing particles of silica, alumina,zirconia, titania, ceria, manganese oxide, iron oxide, etc. using any ofmedium type dispersers, e.g. a bead mill, a ball mill, and a sand mill,stirring type dispersers, e.g. a colloid mill, and an ultrasonicdisperser.

Fine particle dispersions used for chemical/mechanical polishing containfine particles having a primary particle size of from 10 to 100nanometers. A fine particle powder is dispersed in an alkaline or acidicaqueous solution. At the same time as the powder is dispersed, anelectrical double layer is formed near the surfaces of the fineparticles by ions in the aqueous solution, and the ζ-potential of theparticles in the slurry reduces. Accordingly, the attractive forcesbetween the particles increase, causing an agglomeration phenomenon tooccur. Consequently, the particles reach a stable state in the form ofagglomerates of the order of from 300 micrometers to 1 millimeter insize. In the present semiconductor manufacturing process, a particlesize of 140 to 200 nanometers in terms of center particle size isdemanded for fine particle dispersions used in chemical/mechanicalpolishing, and the breadth of the particle size distribution demanded isfrom 100 to 400 nanometers. Therefore, the agglomerates need to beredispersed by some method.

When only a stirring type disperser is used to redisperse the fineparticles for polishing, most of the agglomerates cannot be redispersedeven if the treatment is carried out for a considerably long period oftime.

In the case of a fine particle dispersion for chemical/mechanicalpolishing that uses silica particles as an abrasive, an alkalinesolution prepared by dissolving potassium hydroxide in ultrapure wateris mixed with 13% to 25% by weight of silica having a primary particlesize of from 20 to 30 nanometers to obtain a dispersion. The obtaineddispersion is stirred at high speed for 1 hour at 3,000 rpm and furthersubjected to dispersing treatment for 1 hour at 1,400 rpm in a bead millusing beads having a diameter of 2 millimeters, thereby obtaining a fineparticle dispersion for polishing that has a center particle size of 230nanometers and a viscosity of 6 to 10 mPa·s.

In the case of using a medium type disperser, e.g. a ball mill, a fineparticle dispersion having a center particle size of the order of 200nanometers and a particle size distribution breadth of from 150 to 700nanometers is obtained. Thus, it is difficult to obtain a sharp particlesize distribution. In addition, as the period of time of treatmentbecomes longer, the medium itself is worn by a larger amount, causingthe fine particle dispersion to be contaminated. This may lead tocontamination of semiconductor devices.

Fine particle dispersions obtained by the above-described dispersingmethod differ in treating characteristics for each batch of agent owingto the change with time. Consequently, it is impossible to provideconsistency in polishing results. Moreover, there is a problem that theslurry settles in a tank for supplying an amount of abrasive slurrysufficient to polish a number of wafers for one day, which is known as a“day tank”; therefore, it is essential to discharge the slurry from thetank to the outside and dispose of it.

High-purity fine particles are also demanded in the fields of paper,cosmetics, paint, food and so forth. In the field of paper industry, forexample, it is demanded that fine particles used as an inner fillingmaterial and surface modifying material should be purified to a higherlevel. In addition, the use of a highly concentrated fine particledispersion is demanded in order to obtain high paper quality.

In fine particle dispersions used as food additives, it is also demandedto improve absorptivity by atomization and to obtain contamination-freefine particles.

However, it is extremely difficult to obtain a fine particle dispersionin which fine particles are stable in a suspension state. Accordingly, amethod of obtaining a high-purity fine particle dispersion within ashort period of time without using particles or the like for dispersionhas been demanded.

When a fine particle dispersion of a single composition or a pluralityof compositions is suspended in a suspending medium suitable therefor,fine particles often float on the surface of the suspending mediumwithout sinking into it in the case of an ordinary introducing andstirring method because fine particles have a large surface area andhence an extremely small bulk specific gravity in comparison to the truespecific gravity.

When a fine particle dispersion of a single composition or a pluralityof compositions is suspended in either a suspending medium unsuitabletherefor, or when a fine particle dispersion of a plurality ofcompositions of different nature is suspended in either of thesuspending mediums, even if the fine particles are introduced into thesuspending medium, a considerably long time is required to obtain auniform predispersion in the case of preliminary stirring by a stirringmachine or the like. Consequently, the fine particles undesirablyagglomerate before it is sufficiently stirred in the suspending medium.Thus, it is difficult to obtain a uniform predispersion.

Under these circumstances, Japanese Patent Application UnexaminedPublication (KOKAI) Nos. 10-310415 and 11-57521 disclose a method inwhich fine particles are predispersed in water while being sucked by apowder introducing and mixing disperser (trade name: Jet Stream Mixer).According to the method, fine particles are introduced directly into adispersing medium and stirred at the same time to perform preliminarydispersion. In this method, blades for stirring are rotated at highspeed to produce a negative pressure to introduce fine particlestogether with air. Such a system uses an apparatus in which alubricating oil is used in the rotating shaft part to allow the stirringblades to stably rotate at high speed.

FIG. 12 is a diagram illustrating a conventional suction stirringapparatus.

A suction stirring apparatus 71 is installed in a suspension tank 72. Arotor 74 connected to a rotating shaft 73 is rotated at high speed by amotor 75. As a result, a negative pressure is formed in the vicinity ofthe rotor in a suspending medium 76, causing fine particles 78 in a fineparticle storage tank 77 to be sucked through a suction flow path 79,which is formed around the rotating shaft 73, and injected into thesuspending medium 76 in the suspension tank 72. In addition, acylindrical stator 80 is formed around the rotor 74 to induce acirculating flow 81 circulating through the inside and outside of thecylindrical stator 80. Thus, mixed dispersing is performed by thecirculating flow 81 and the shearing force of the rotor 74.

In order to ensure the suction flow path 79 to suck fine particlestogether with air, the apparatus needs to prevent air from flowingthereinto through any portion except a duct 82 for introducing fineparticles. Accordingly, the upper portion of the rotating shaft has ahermetically sealed structure. A hermetic structure using a mechanicalseal is used for a bearing portion 83 that rotates at high speed, i.e.from 3,000 to 4,000 RPM.

As a mechanical seal used in such a bearing portion, it is essential touse an oil-filled seal because the bearing portion is a part thatrotates at high speed. An oil-filled mechanical seal cannot prevent theoil filled therein from penetrating along the rotating shaft by theaction of a negative pressure produced in the pipe as the rotating shaftrotates. Therefore, it is difficult to completely prevent oil fromadhering to fine particles when the particles pass through the suctionflow path formed around the rotating shaft. Thus, the oil-filledmechanical seal suffers from the problem that a high-puritypredispersion cannot be obtained.

Moreover, when fine particles are sucked, air is also introducedtogether with the fine particles. Consequently, air undesirably remainsas fine bubbles in the suspension. Therefore, if it is intended todisperse the predispersion through collision under pressure withoutusing particles for dispersion, the bubbles in the suspensionundesirably act as a buffer, reducing the pressurizing efficiency, andthus making it difficult to disperse the predispersion satisfactorily.

If it is intended to disperse the predispersed suspension to a highdegree by a dispersing apparatus using particles for dispersion, e.g. abead mill, a ball mill, or a sand mill, an extremely long time isrequired. Consequently, contaminants are generated from the particlesfor dispersion, causing the purity to be reduced. Moreover, it isdifficult to obtain a dispersion in which fine particles are uniformlydispersed.

Accordingly, methods of producing a dispersion without using particlesfor dispersion are proposed, for example, in Japanese Patent ApplicationUnexamined Publication (KOKAI) Nos. 9-193004, 9-142827, 10-310415 and11-57521. Dispersing methods employed in these methods use dispersingapparatus based on a high-pressure impact system, an opposed impactsystem, etc. The first system is arranged to obtain a fine particledispersion by jetting out a predispersed fine particle suspension from anozzle under high pressure so that the fine particle suspension collidesagainst a plate having a high hardness (trade name, Manton-GaulinHomogenizer: Doei Shoji). With this system, however, the plate memberwears out at a high rate, and consequently, the problem of contaminationcannot be solved. The second system is arranged to obtain a fineparticle dispersion as follows. After a high pressure has been appliedto a predispersed fine particle suspension, the flow path is branched,and after the fine particle suspension has been once made to collideagainst a plate member, the branched flow paths are changed in directionthrough 90 degrees so that fine particle dispersions collide with eachother (trade name, Microfluidizer: Mizuho Kogyo; Nanomizer: TsukishimaKikai; Genus PY: Hakusui Kagaku Kogyo, etc.). However, in the process ofchanging the flow path through 90 degrees by collision after branchingthe flow path under high pressure, impact caused by the collisionagainst the plate member is large. Even when diamond is used, durabilityis very low. Moreover, the increase in throughput capacity isunfavorably limited by a structural problem.

According to a third system, after a high pressure has been applied to apredispersed fine particle suspension, the flow path is branched intotwo, and fine particle suspensions are made to collide with each otherdirectly by nozzles opposed to each other, thereby obtaining a fineparticle dispersion (trade name, Ultimizer: Karasawa Fine). The thirdsystem is superior to the first and second systems. However, it ispractically impossible to oppose two nozzles to each other at apredetermined distance so that the nozzles are completely parallel toeach other and the center lines of the nozzles are completely coincidentwith each other. Thus, there have been problems to be solved in terms ofthe generation of contaminants, mass productivity, durability, etc.

An object of the present invention is to provide a method of producing ahigh-purity fine particle dispersion without using a particulatesubstance for dispersion, the method being capable of producingcontaminant-free high-purity fine particles within a reduced period oftime. Another object of the present invention is to provide a method ofproducing a fine particle dispersion of favorable dispersion stabilitythat will not thicken to gel or form a precipitate even if it is storedfor a long period of time.

DISCLOSURE OF THE INVENTION

The present invention is a method of producing a fine particledispersion characterized by having a dispersing step where, after fineparticles have been sucked into a dispersing medium to prepare asuspension by a suction type stirring machine and bubbles have beenremoved from the suspension by a bubble removing means, the suspensionis pressurized and introduced from opposite directions so as to collidewith each other, thereby dispersing the suspension.

In the above-described method of producing a fine particle dispersion,the suction-stirring machine is arranged such that only a flow path foran air flow is formed in a space where a rotating shaft is exposed, anda flow path for fine particles is formed outside the flow path for anair flow.

In the above-described method of producing a fine particle dispersion,the bubble removing means is a cyclone type bubble removing means.

In the above-described method of producing a fine particle dispersion, adispersing means capable of adjusting a center axis of a dispersingnozzle is used as one of two dispersing nozzles in the dispersing step.

In the above-described method of producing a fine particle dispersion, adispersing means having a dispersing nozzle in which the cross-sectionalarea gradually increases from the inlet side thereof toward the outletside thereof is used in the dispersing step.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a method of producing a high-purityfine particle dispersion without using particles for dispersionaccording to the present invention.

FIG. 2 is a diagram illustrating an example of a suction stirringapparatus usable in the predispersing step of the present invention.

FIG. 3 is a diagram illustrating an example of a bubble removingapparatus used in the method of the present invention.

FIG. 4 is a diagram illustrating an opposed impact type dispersingapparatus used in the method of producing a fine particle dispersionaccording to the present invention.

FIG. 5 is a diagram illustrating an opposed impact type dispersingapparatus used in the method of producing a fine particle dispersionaccording to the present invention.

FIG. 6 is a diagram illustrating the sectional configuration of a nozzleand the condition of presence of solid particles in a solid-liquidmultiphase fluid.

FIG. 7 is a diagram illustrating an example of dispersing nozzles.

FIG. 8 is a diagram illustrating the particle size distribution of apredispersion obtained.

FIG. 9 is a diagram illustrating the change with time of the particlesize distribution of a dispersion obtained.

FIG. 10 is a diagram illustrating the change with time of the particlesize distribution of a dispersion obtained.

FIG. 11 is a diagram illustrating the change with time of the particlesize distribution of a dispersion obtained.

FIG. 12 is a diagram illustrating a conventional suction stirringapparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

The method of producing a high-purity fine particles without usingparticles for dispersion according to the present invention can becarried out by using a mixing means capable of rapid mixing withoutintroducing a contaminant into a liquid and further using a bubbleremoving means for removing bubbles introduced into the liquid duringmixing and an opposed impact type dispersing means having excellentdispersibility.

Accordingly, the method of the present invention uses a suction stirringmachine having a structure free from generation of a contaminant fromthe device body as a means for forming a hydrophobic or hydrophilic fineparticle material of a single or plurality of compositions or a fineparticle material of a plurality of compositions of both hydrophobic andhydrophilic natures, which is fit for the purpose, into an aqueous ornonaqueous suspension before it is highly dispersed. By using thesuction stirring machine, the fine particle material is sucked andreleased into water or a nonaqueous solvent, and at the same time,stirring is carried out, thereby obtaining an extremely stablepredispersion without using a dispersant regardless of the physicalproperties of the combination of particles and a liquid for suspension.

The obtained predispersion contains a large number of fine bubblesbecause of the suction of fine particles by the suction stirringmachine. The bubbles constitute a serious obstacle to the pressurizingstep. It was impossible to remove the bubbles completely even when thepredispersion was allowed to stand for a considerably long period oftime.

Accordingly, the highly dispersing method of the present invention isbased on the finding that loss in the pressurizing step can be preventedby applying a high pressure to the suspension after fine bubbles havebeen removed by the debubbling means.

In addition, the highly dispersing method of the present invention isbased on the finding that if the suspensions are made to collide witheach other after the position of one of two opposed impact type nozzleshas been precisely adjusted, the liquids surely collide with each other;therefore, no contaminant is generated from the equipment, and ahigh-purity highly dispersed fine particle dispersion can be obtained.

Furthermore, the present inventor found that it is possible to obtain ahigh-purity fine particle dispersion rapidly, safely and hygienicallyand to maintain the stability thereof for a long period of time byusing, as the opposed impact type nozzles, nozzles capable of varyingthe size of particles to be produced under the same pressure conditionsby changing the configuration of the nozzles according to thecharacteristics of the fluid or according to the necessary conditions.

The present invention will be described below with reference to thedrawings.

FIG. 1 is a diagram illustrating the process of producing a high-purityfine particle dispersion without using particles for dispersionaccording to the present invention.

At a predispersing step A, a fine particle material of a single orplurality of compositions is continuously introduced into a suspendingliquid, and at the same time, predispersion is carried out by shearingforce. Next, the predispersed suspension is continuously debubbled at abubble removing step B to remove fine bubbles.

Next, at a main dispersing step C, predispersed suspensions after thedebubbling are made to collide with each other to effect dispersion,thereby obtaining a high-purity particle dispersion without usingparticles for dispersion.

FIG. 2 is a diagram illustrating an example of suction stirringapparatus usable in the predispersing step of the present invention.

A suction stirring apparatus 1 is installed in a suspension tank 3containing a suspending medium 2. A rotor 6 is secured to a rotatingshaft 5 connected to a motor 4. As the rotating shaft 5 rotates, anegative pressure is produced in the vicinity of the rotor 6. Thisinduces an air flow 8 passing through an air flow passage 7 formedaround the rotating shaft 5. Consequently, a negative pressure isproduced in an air nozzle portion 9 at the distal end of the air flowpassage 7. These negative pressures cause fine particles 11 in a fineparticle storage tank 10 to be supplied through a fine particle passage12, which is formed outside the air flow passage, and injected into thesuspending medium 2 from a fine particle nozzle 13 at the distal end.Furthermore, a cylindrical stator 14 is provided to surround theabove-described members. Therefore, a circulating flow 15 is formedinside and outside the stator. Dispersion is effected by large shearingforce generated between the rotor and the stator. Shearing and swirlingby a swirling flow induced inside and outside the stator are repeated toperform desired predispersion.

In the suction stirring apparatus, fine particles are sucked through aduct and stirred. Therefore, there is no likelihood that fine particlesmay scatter to contaminate the ambient atmosphere. However, because fineparticles are conveyed by using an air flow, a large amount of air ispresent in the obtained predispersion in the form of fine bubbles. Ifthe predispersion with fine bubbles suspended therein is used in thesubsequent step, the fine bubbles may give rise to a problem. Inaddition, when the predispersion is pressurized to disperse it to a highdegree by a method, for example, an opposed impact method, the finebubbles undesirably act as a buffer because the compressibility ofbubbles is higher than that of a liquid. Consequently, it becomesdifficult to pressurize the predispersion satisfactorily.

Accordingly, the method of the present invention has the step ofremoving bubbles from the bubble-containing predispersion.

FIG. 3 is a diagram illustrating an example of bubble removing apparatusused in the method of the present invention. FIG. 2(A) shows a verticalsectional view, and FIG. 2(B) shows a horizontal sectional view.

A bubble removing apparatus 20 shown in FIG. 3 has an inlet 21 for abubble-containing predispersion in the bottom thereof and a conicalcyclone chamber 22 therein. A bubble-containing predispersion flowing inthrough the inlet 21 is changed into a swirling flow 24 in a preliminaryswirling flow chamber 23. The bubble-containing predispersion flowing incontinuously is accelerated as it is pushed upwardly in the cyclonechamber 22. By centrifugal force occurring at that time, thepredispersion 25, which has a high density, is caused to move to anouter peripheral chamber 27 through a large number of fine holes 26provided in the upper part of the cyclone chamber 22. Thus, thepredispersion having bubbles removed therefrom is taken out from anoutlet 28 in the top. On the other hand, fine bubbles, which have a lowdensity, gather in the center of the cyclone chamber and are dischargedto the outside through a bubble discharge opening 30 from a bubbleremoving pipe 29 provided with a large number of holes, which isprovided in the center of the cyclone chamber.

The use of a bubble removing apparatus having a cyclone chamber, asshown in this example, allows bubbles to be removed instantaneously andmakes it possible to obtain a debubbled predispersion continuously.

Next, in the opposed impact type dispersing apparatus proposed by thepresent inventor (trade name: Ultimizer System, Japanese Patent Number2,553,287; U.S. Pat. No. 5,380,089) or the like, a high pressure isapplied to the predispersed fine particle suspension, and thereafter,the flow path is branched into two, and fine particle suspensions aremade to collide with each other directly by nozzles opposed to eachother. Thus, a highly dispersed fine particle dispersion can be obtainedin large quantities without generating a contaminant.

FIG. 4 is a diagram illustrating an opposed impact type dispersingapparatus used in the fine particle dispersion producing method of thepresent invention.

A dispersing apparatus body 31 capable of enduring a high-pressurepredispersion supplied to the dispersing apparatus has a space providedtherein. A dispersing unit 34 is provided between metal seal members 32and 33 in the space. A conversion coupling 35 is fastened by a coupler36 provided with right- and left-hand threads.

A predispersion to be dispersed is pressurized by a high-pressure pumpto enter one inlet passage 37 in the pressure vessel body and flow intoan inlet port 38 in the dispersing unit. The inner diameter of the inletport 38 is smaller than that of the inlet passage 37. Meanwhile, apredispersion is supplied under pressure from a conversion coupling-sideinlet passage 39 so as to pass through the metal seal member and flowinto the other inlet port 40 in the dispersing unit. The inner diameterof the inlet port 40 is smaller than that of the inlet passage 39. Thus,dispersion is carried out by collision between the predispersionssupplied at high speed from the opposite directions to each other. Afterthe dispersion has been carried out, the fine particle dispersion passesthrough an outlet port 41 and is taken out from an outlet passage 42.

The dispersing unit is kept in plane contact with the planar portions ofthe metal seal members to maintain a hermetic state in the high-pressurevessel by the fastening force of the conversion coupling. On the otherhand, the outlet side of the emulsifying unit is provided with an O-ring43 to prevent leakage.

In such an opposed impact type dispersing apparatus, if the dispersingunit is increased in size to allow an increased amount of predispersionto be treated and the left and right nozzles are made of a superhardsubstance, e.g. diamond, and opposed to each other, there may be caseswhere the center axes of the left and right nozzles cannot be madecoincide with each other simply by fastening. If the center axes are notcoincident with each other, the durability of the dispersing unitdegrades. Moreover, fine particles arising from the wear of thedispersing unit may cause the quality of the product to be degraded as acontaminant.

In the impact dispersion type dispersing apparatus, however, because thepressure handled is high, each member is precisely machined, and thecontact surfaces of the members are kept in plane contact with eachother. In this state, the members are kept hermetic. Thus, the degree ofcoincidence between the center axes of the dispersing nozzles depends onthe accuracy of each member and the assembly accuracy. Adjustment of thecenter axes or other similar means has not heretofore been used.

In the following apparatus, the center axis of one of the dispersingnozzles is finely adjustable, thereby allowing the center axes of thetwo dispersing nozzles to be made coincident with each other with highaccuracy.

FIG. 5 is a diagram illustrating an opposed impact type dispersingapparatus used in the method of producing a fine particle dispersionaccording to the present invention.

A dispersing apparatus body 51 withstanding high pressure has adispersing nozzle retainer 52 a provided in a space therein. Thedispersing nozzle retainer 52 a retains one dispersing nozzle 53 atherein. A cylindrical dispersing nozzle fixing member 54 a havingtherein a passage for a fluid to be dispersed, a dispersing nozzlefixing member 54 a and a cylindrical fastening member 55 a havingtherein a passage for a fluid to be dispersed are successively disposedon the fluid supply side of the dispersing nozzle 53 a. These membersare fastened to the dispersing apparatus body 51 by using a thread 56 aprovided on the outer surface of the fastening member 55 a. Thus, themembers are brought into plane contact with each other and fixed in ahermetic state.

The other dispersing nozzle 53 b is opposed to the fixed dispersingnozzle 53 a and retained in a dispersing nozzle retainer 52 b. Acylindrical dispersing nozzle fixing member 54 b having therein apassage for a fluid to be dispersed and a dispersing nozzle adjustingmember 57 having therein a passage for a fluid to be dispersed aresuccessively disposed on the fluid supply side of the dispersing nozzle53 b. The dispersing nozzle adjusting member 57 is arranged to securethe dispersing nozzle 53 a and the dispersing nozzle fixing member 54 bto the dispersing nozzle retainer 52 b by tightening adjusting bolts 59with respect to a plurality of adjusting thread portions 58 provided onthe dispersing nozzle retainer 52 b at respective positions equallyspaced circumferentially.

When the dispersing nozzle adjusting member 57 is fixed by the pluralityof adjusting thread portions 58 and the adjusting bolts 59, the positionof the dispersing nozzle 53 a and dispersing nozzle fixing member 54 bcan be slightly displaced by adjusting the tightening torque applied toeach individual adjusting bolt 59. There may be cases where the contactsurface of the fluid supply side of the dispersing nozzle fixing member54 b and the contact surface of the dispersing nozzle adjusting member57 cannot be brought into complete plane contact with each other byadjusting the tightening torque of the adjusting bolts 59. However, anO-ring 60 or other hermeticity maintaining means is provided on thefluid supply side of the dispersing nozzle fixing member. Thus, thefluid supply surface side of the dispersing nozzle fixing member 54 band the dispersing nozzle adjusting member 57 are kept in a hermeticstate.

Further, on the fluid supply side of the dispersing nozzle adjustingmember 57, the dispersing nozzle adjusting member 57 and a cylindricalfastening member 55 b having therein a passage for a fluid to bedispersed are successively disposed, and the dispersing nozzle adjustingmember 57 is fastened by engagement between a thread 56 b provided onthe outer surface of the fastening member 55 b and a thread provided onthe dispersing apparatus body 51 and thus fixed at a predeterminedposition in the dispersing apparatus body 51. There may be cases wherethe contact surface of the fluid supply side of the dispersing nozzleadjusting member 57 and the contact surface of the fastening member 55 bcannot be brought into complete plane contact with each other. However,an O-ring 61 or other hermeticity maintaining means is provided on thefastening member 55 b. Therefore, hermeticity is maintained.

The fastening members 55 a and 55 b are provided with respective inlets62 a and 62 b for a pressurized fluid. Fluids flowing in through theinlets 62 a and 62 b are jetted out from the dispersing nozzles 53 a and53 b whose center axes are coincident with each other. Thus, the fluidscollide with each other, thereby being dispersed to a high degree. Then,the dispersed fluid is taken out from an outlet 63.

The degree of coincidence between the center axes of the dispersingnozzles 53 a and 53 b can be confirmed by supplying water under apressure of several MPa in a state where a plug 64 is removed from thedispersing apparatus body 51, and making a check as to whether or notthe water jetted out from the dispersing nozzles 53 a and 53 b shows adisk-shaped locus that is right-angled over the whole circumference byhead-on collision.

For example, assuming that the spacing between the dispersing nozzles 53a and 53 b is 4 millimeters, if the sum total of the parallelism betweenthe respective surfaces of the dispersing nozzles and an eccentricitydue to the gaps between the dispersing nozzles 53 a and 53 b on the onehand and the dispersing nozzle retainers 52 a and 52 b on the other is1°, 30′, or 15′, the tolerance is eliminated by adjusting by 3.49micrometers, 1.74 micrometers, or 0.87 micrometers. Thus, the centeraxes of the two dispersing nozzles can be made coincident with eachother.

A fine particle dispersing nozzle used in a dispersing apparatus isgenerally designed to maximize the flow rate and moreover arranged suchthat, as proposed in Japanese Patent Number 2,587,895 (U.S. Pat. No.5,380,089) by the present inventor, the cross-sectional area of anorifice is gradually reduced in a curve from the inlet side of thenozzle to the minimum orifice diameter portion so that an area whereonly a liquid is present is formed around a solid-liquid multiphase flowthat has passed the minimum orifice diameter portion. The use of such anozzle makes it possible to prevent collision of solid particles againstthe wall surface and to obtain a nozzle of high durability.

FIG. 6 is a diagram illustrating the sectional configuration of a nozzleand the condition of presence of solid particles in a solid-liquidmultiphase fluid. In a case where an orifice is formed between the inletside and the outlet side, the cross-sectional area of the duct isgradually reduced toward the orifice. More specifically, in the exampleshown in FIG. 5, the inlet side is formed from a duct of 1 millimeter insize, and the cross-sectional area of the duct is gradually reduced toan orifice diameter of 0.3 millimeters over a length of 0.52millimeters.

Consequently, a boundary particle streamline that defines an area whereno particles are present is formed by the orifice. The axis of abscissarepresents the length of the nozzle on the assumption that the orificeradius is 1, and the axis of ordinate represents the diameter of theduct on the assumption that the orifice radius is 1. Because a partwhere no particles are present is formed on the outlet side of theorifice in the nozzle, the nozzle can be prevented from wearing byforming the wall surface more away from the center axis than theboundary particle streamline.

Meanwhile, the present inventor found that the use of an orifice whosecross-sectional area gradually increases as a dispersing nozzle allowsextremely fine particles to be obtained, although the flow rate isreduced. Accordingly, the purpose of obtaining fine particles with anextremely small particle size can be attained by using a dispersingnozzle whose cross-sectional area gradually increases.

FIG. 7 illustrates an example of dispersing nozzles.

FIG. 7(A) is a diagram illustrating a nozzle exhibiting a high flowrate. A fluid entering a dispersing nozzle 53 from an inlet side 53 csuffers a loss owing to the gradual reduction in the cross-sectionalarea. However, because the flow velocity is sufficiently high, the lossof head can be ignored. Thus, the maximum flow rate can be obtained.

On the other hand, in the case of using a dispersing nozzle in which, asshown in FIG. 7(B), the area of the inlet side 53 c is reduced, andwhich has such an orifice diameter that the area gradually increases inreverse relation to FIG. 7(A), it is possible to obtain fine particleshaving a smaller size than in the case of FIG. 7(A), although the flowrate becomes lower than in the case of the nozzle shown in FIG. 7(A).

EXAMPLES

Examples of the present invention will be shown below to describe thepresent invention.

(Preparation of a predispersion)

Into 70 kg of pure water, fumed silica having a specific surface area of50 to 380 g/cm² and a primary particle size of 7 to 30 nanometers wassucked in varying amounts and stirred with a suction stirring apparatushaving a rotor diameter of 160 millimeters, a stator inner diameter of170 millimeters, a rotating shaft diameter of 260 millimeters, an airflow duct inner diameter of 300 millimeters, an air flow duct outerdiameter of 310 millimeters, a fine particle passage inner diameter of350 millimeters and a fine particle suction pipe inner diameter of 30millimeters. Thereafter, bubbles were removed by a cyclone type bubbleremoving apparatus.

The viscosity of the predispersion obtained was 120 cP. The particlesize distribution of a predispersion having a concentration of 30% byweight was measured with a laser beam diffraction type particle sizedistribution measuring apparatus (SALD-2000A, manufactured by ShimadzuCorporation). The result of the measurement is shown in FIG. 8.

Example 1

To ultrapure water, potassium hydroxide was added as a pH adjustor toprepare an alkaline solution having a pH of 11. Into the alkalinesolution, fumed silica was introduced in three different amounts, i.e.12.5% by weight, 25% by weight, and 60% by weight, with a suctionstirring machine to prepare three different predispersions.

Next, the predispersions were each treated in two different numbers ofpasses, i.e. 1 pass and 3 passes, under 200 MPa with a dispersingapparatus (Ultimizer System HJP-25028, manufactured by Sugino Machine)having the dispersing nozzle shown in FIG. 4, thereby preparing 6dispersions in total. The particle size of fine particles in eachdispersion and the particle size distribution thereof were measured witha laser beam diffraction type particle size distribution measuringapparatus (SALD-2000A, manufactured by Shimadzu Corporation). The resultof the measurement is shown in FIG. 8. The treating conditions of eachsample and the characteristics of the particles obtained are shown inTable 1 below.

TABLE 1 Oxide Breadth of Center concen- Treating Number particle sizeparticle Foreign tration pressure of distribution size matter (wt %)(MPa) passes (nm) (nm) (ppb) 12.5 200 1 180-530 178 not detected 12.5200 3  80-340 156 not detected 25 200 1  80-530 178 not detected 25 2003  80-340 156 not detected 60 200 1 100-500 198 not detected 60 200 3 80-410 180 not detected

Next, a container containing each dispersion obtained was stored at 25°C., and 0.2 milliliters of the dispersion was sampled from each of threedifferent layers of the dispersion in the container, i.e. the top (alayer 10 millimeter from the liquid surface), the middle (a layer 100millimeters from the liquid surface), and the bottom (a layer 190millimeters from the liquid surface), every month to measure theparticle size distribution of fine particles with a laser beamdiffraction type particle size distribution measuring apparatus(SALD-2000A, manufactured by Shimadzu Corporation). The results of themeasurement are shown in FIG. 9 (raw material: 12.5% by weight), FIG. 10(raw material: 25% by weight) and FIG. 11 (raw material: 60% by weight).In each of these figures: (A) shows the particle size distribution inthe top; (B) shows the particle size distribution in the middle; and (C)shows the particle size distribution in the bottom. The axis of abscissarepresents the number of months of storage.

Example 2

Into ultrapure water, aluminum oxide having a center particle size of 13nanometers and a specific surface area of 100 m²/g was introduced inthree different amounts, i.e. 12.5% by weight, 25% by weight, and 60% byweight, with a suction stirring machine to prepare three differentpredispersions.

Next, the predispersions were each treated in 3 passes under 200 MPawith a dispersing apparatus (Ultimizer System HJP-25028, manufactured bySugino Machine) having the dispersing nozzle shown in FIG. 4 to preparedispersions, and the particle size of fine particles in each dispersionand the particle size distribution thereof were measured with a laserbeam diffraction type particle size distribution measuring apparatus(SALD-2000A, manufactured by Shimadzu Corporation). The treatingconditions of each sample and the characteristics of the particlesobtained are shown in Table 2 below.

TABLE 2 Oxide Breadth of Center concen- Treating Number particle sizeparticle Foreign tration pressure of distribution size matter (wt %)(MPa) passes (nm) (nm) (ppb) 12.5 200 3 65-300 158 not detected 25 200 368-330 162 not detected 60 200 3 72-360 170 not detected

Example 3

Into ultrapure water, aluminum oxide having a center particle size of 21nanometers and a specific surface area of 50 m²/g was introduced in twodifferent amounts, i.e. 30% by weight, and 60% by weight, with a suctionstirring machine to prepare two different predispersions.

Next, the predispersions were each treated in 3 passes under 200 MPawith a dispersing apparatus (Ultimizer System HJP-25028, manufactured bySugino Machine) having the dispersing nozzle shown in FIG. 4, to preparedispersions, and the particle size of fine particles in each dispersionand the particle size distribution thereof were measured with a laserbeam diffraction type particle size distribution measuring apparatus(SALD-2000A, manufactured by Shimadzu Corporation). The treatingconditions of each sample and the characteristics of the particlesobtained are shown in Table 3 below.

TABLE 3 Oxide Breadth of Center concen- Treating Number particle sizeparticle Foreign tration pressure of distribution size matter (wt %)(MPa) passes (nm) (nm) (ppb) 35 220 3 156-556 440 not detected 60 220 3160-576 457 not detected

Example 4

Next, the predispersions were each treated in 3 passes under 200 MPawith a dispersing apparatus (Ultimizer System HJP-25028, manufactured bySugino Machine) having the same dispersing nozzle as shown in FIG. 4except that the suction opening and the discharge opening of thedispersing nozzle were installed in reverse relation to that in FIG. 4and that the diameter of the suction opening was 0.2 millimeters and thediameter of the discharge opening was 0.2 millimeters, to prepare 3dispersions in total, and the particle size of fine particles in eachdispersion and the particle size distribution thereof were measured witha laser beam diffraction type particle size distribution measuringapparatus (SALD-2000A, manufactured by Shimadzu Corporation). Thetreating conditions of each sample and the characteristics of theparticles obtained are shown in Table 4 below.

TABLE 4 Oxide Breadth of Center concen- Treating Number particle sizeparticle Foreign tration pressure of distribution size matter (wt %)(MPa) passes (nm) (nm) (ppb) 12.5 200 3 30-210 80 not detected 25 200 330-210 78 not detected 60 200 3 30-230 79 not detected

Industrial Applicability

A fine particle dispersion produced by the method of the presentinvention has a uniform particle size and a narrow particle sizedistribution breadth. Thus, a high-purity and uniform fine particledispersion can be obtained. Accordingly, the present invention exhibitssignificant effects in various use applications, including the processof smoothing and planarizing oxide films, e.g. interlayer insulatorfilms, and metal wiring films in the semiconductor manufacturingprocess.

What is claimed is:
 1. A method of producing a fine particle dispersioncharacterized by having a dispersing step where, after fine particleshave been sucked into a dispersing medium to prepare a suspension by asuction stirring machine and bubbles have been removed from thesuspension by a bubble removing means, the suspension is pressurized andintroduced from opposite directions so as to collide with each other,thereby dispersing the suspension.
 2. A method of producing a fineparticle dispersion according to claim 1, wherein in the suctionstirring machine, only a flow path for an air flow is formed in a spacewhere a rotating shaft is exposed, and a flow path for fine particles isformed outside the flow path for an air flow.
 3. A method of producing afine particle dispersion according to either of claims 1 or 2, whereinthe bubble removing means is a cyclone bubble removing means.
 4. Amethod of producing a fine particle dispersion according to any one ofclaims 1 and 2, wherein a dispersing means capable of adjusting a centeraxis of a dispersing nozzle is used as one of two dispersing nozzles inthe dispersing step.
 5. A method of producing a fine particle dispersionaccording to any one of claims 1 and 2, wherein a dispersing meanshaving a dispersing nozzle in which a cross-sectional area graduallyincreases from an inlet side thereof toward an outlet side thereof isused in the dispersing step.